High voltage device having Schottky diode

ABSTRACT

A high voltage device having a Schottky diode integrated with a MOS transistor includes a semiconductor substrate a Schottky diode formed on the semiconductor substrate, at least a first doped region having a first conductive type formed in the semiconductor substrate and under the Schottky diode, and a control gate covering a portion of the Schottky diode and the first doped region positioned on the semiconductor substrate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a high voltage device having a Schottky diode,and to a high voltage device having a Schottky diode integrated with ametal-oxide-semiconductor (MOS) transistor.

2. Description of the Prior Art

Power devices are required to be fast switching and sustainable to highvoltage of hundreds Volts (V). Therefore high voltage (HV) devices suchas HV metal-oxide-semiconductor (HVMOS) transistor, insulated gatebipolar transistor (IGBT), and Schottky diode which have high-speedswitching characteristics have been developed and commonly used forpower conversion, power control, and so forth of the power system ininstruments such as home appliances, communication devices and controldevices of in-vehicle motor.

Among those HV devices, Schottky diode's voltage drop at a forward biasof about 1 mA is in the rage of 0.15 V to 0.45 V, while the conventionalsilicon diode is of about 0.6 V. Therefore Schottky diode is morepreferable in voltage-clamping applications and in applications forpreventing transistor saturation.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda high voltage device having Schottky diode. The high voltage deviceincludes a semiconductor substrate, at least a dielectric region formedin the semiconductor substrate, a Schottky diode formed on thesemiconductor substrate, at least a salicide block (SAB) positioned onthe semiconductor substrate, and at least a first heavily doped regionhaving a first conductive type formed in the semiconductor substrateunder the SAB. The first heavily doped region is non-contacting with theSchottky diode.

According to a second aspect of the present invention, there is provideda high voltage device having Schottky diode. The high voltage deviceincludes a semiconductor substrate, a Schottky diode formed on thesemiconductor substrate, at least a first doped region having a firstconductive type formed in the semiconductor substrate and under theSchottky diode, and a control gate positioned on the semiconductorsubstrate. The control gate covers a portion of the Schottky diode andthe first doped region positioned on the semiconductor substrate.

According to the high voltage device having the Schottky diode providedby the present invention, the advantage features of the presentinvention includes high operating voltage and prevention of leakagecurrent due to the provided first heavily doped region. According toanother high voltage device having the Schottky diode integrated withthe MOS transistor, the advantage features of the present inventionincludes improved turn-on speed and thus such high voltage devicerenders a protection function.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of a cross-sectional view of a highvoltage device having a Schottky diode provided by a first preferredembodiment of the present invention;

FIG. 2 is a modification to the high voltage device of the firstpreferred embodiment;

FIG. 3 is a schematic drawing of a cross-sectional view of a highvoltage device having a Schottky diode integrated with a MOS transistorprovided by a second preferred embodiment of the present invention; and

FIG. 4 is a schematic drawing of a cross-sectional view of a highvoltage device having a Schottky diode provided by a third preferredembodiment of the present invention.

DETAILED DESCRIPTION

Please refer to FIG. 1, which is a schematic drawing of across-sectional view of a high voltage device having a Schottky diodeprovided by a first preferred embodiment of the present invention. Asshown in FIG. 1, a high voltage device 100 includes a semiconductorsubstrate 102 is provided. The semiconductor substrate 102 is formed ofsemiconductor material having a first conductive type and the firstconductive type preferably is a p-type, but not limited to this. Thehigh voltage device 100 also includes a well region 104 having a secondconductive type, that is an n-type in this preferred embodiment, formedin the semiconductor substrate 102. The well region 104 serves as adrift region that permits a more gradual voltage drop across theterminals and reduces the possibility of avalanche breakdown in thisarea of the high voltage device 100. Therefore the doping concentrationof the well region 104 is adjustable according to the requirement to thehigh voltage device 100.

The high voltage device 100 includes a Schottky diode 106 formed on thesemiconductor substrate 102 in the well region 104, a dielectric regionsuch as a localized oxidation isolation (LOCOS) or preferably a shallowtrench isolation (STI) 108 formed in the well region 104 of thesemiconductor substrate 102, at least a salicide block (SAB) 110positioned between the STI 108 and the Schottky diode 106, and at leasta first heavily doped region 112 having the first conductive type, thatis the p-type in this preferred embodiment, formed in well region 104 ofthe semiconductor substrate 100 under the SAB 110. It is noteworthy thatthe first heavily doped region 112 is non-contacting with the Schottkydiode 106. The high voltage device 100 of the preferred embodiment isprovided in a symmetrical configuration as shown in FIG. 1, even in acircular configuration with the Schottky diode 106 at the center and STI108 encircling the Schottky diode 106, but not limited to this.

The high voltage device 100 of the preferred embodiment further includesa second heavily doped region 114 having the second conductive type,which is the n-type according to the preferred embodiment, in the wellregion 104 of the semiconductor substrate 102. The second heavily dopedregion 114 is formed adjacent to the STI 108, and particularly is formedon a side opposite to the Schottky diode 106.

In the preferred embodiment, the Schottky diode 106 includes titaniumsilicide, cobalt silicide, tantalum silicide and combinations thereof.The Schottky diode 106 is formed by performing a self-alignedsilicidation (salicide) process. In the salicide process, the SAB 110 isformed on the semiconductor substrate 102 for preventing a portion ofthe silicon material from being reacted in the salicide process. Then ametal layer (not shown) is formed on the semiconductor substrate 102 andfollowed by performing an anneal treatment to react the metal with theunderlying silicon. Additionally, another salicide layer (not shown) canbe simultaneously formed on the second heavily doped region 114 forimproving Ohmic contact. Since the salicide process is well-known tothose skilled in the art, the details are omitted in the interest ofbrevity.

According to the first preferred embodiment, the Schottky diode 106 andthe second heavily doped region 114 serve as the two terminals forapplying voltages. As mentioned above, when a forward bias is applied,the signal input from the second heavily doped region 114 flows throughthe well region 104 under the STI 108 and reaches the Schottky diode 106with the well region 104 serving as the drift region that permitsvoltage drops as mentioned above. In such a case, the well region 104under STI 108 is regarded as a resistor R. When the high voltage signalpasses through the resistor R, it is converted into an applicable lowvoltage signal. Consequently, the high voltage device 100 provided bythe preferred embodiment has an operating voltage of about 20 Volt.

Furthermore, it is found a leakage current always occurs at the sidewall of the STI 108, therefore the first heavily doped region 112 thatis positioned adjacent to the STI 108 is further provided to preventsaid leakage current.

Please refer to FIG. 2, which is a modification to the high voltagedevice 100 of the first preferred embodiment. According to themodification, the high voltage device 100 further includes a dopedregion 116 having the first conductive type formed under the STI 108 inthe well region 104 of the semiconductor substrate 102 for furtherimproving the operating voltage of the high voltage device 100 of thepreferred embodiment. Because of the doped region 116, the signals areenforced to across a prolonged pathway as shown in FIG. 2. In such acase, when the high voltage signal passes through the resistors R₁, R₂,R₃, which are regarded in series connection, the high voltage signal isconverted into an even lower applicable voltage signal. It is noteworthythat the amount of the resistors merely are exemplarily disclosed, it isadjustable according to the doping depth or doping concentration of thedoped region 116. Accordingly, the well region 104 provides more voltagedrops and thus the high voltage device 100 has improved operatingvoltage.

Accordingly, the high voltage device 100 of the first preferredembodiment provides higher operating voltage and prevention of leakagecurrent due to the first heavily doped region 112.

Please refer to FIG. 3, which is a schematic drawing of across-sectional view of a high voltage device having a Schottky diodeintegrated with a MOS transistor provided by a second preferredembodiment of the present invention. As shown in FIG. 3, a high voltagedevice 200 including a semiconductor substrate 202 is provided. Thesemiconductor substrate 202 includes a first conductive type and thefirst conductive type preferably is a p-type, but not limited to this.The high voltage device 200 also includes a well region 204 having asecond conductive type, that is an n-type in this preferred embodimentformed in the semiconductor substrate 202. The high voltage device 200also includes a Schottky diode 206 formed on the semiconductor substrate202 in the well region 204, at least a doped region 208 having a firstconductive type formed in the well region 204 of the semiconductorsubstrate 202 and under the Schottky diode 206, a control gate 210positioned on the semiconductor substrate 204, a dielectric region suchas a LOCOS or preferably a STI 220 formed in the well region 204 of thesemiconductor substrate 202, and a SAB 222 formed on the semiconductorsubstrate 202.

In the preferred embodiment, the Schottky diode 206 includes titaniumsilicide, cobalt silicide, tantalum silicide and combinations thereof.The Schottky diode 206 is also formed by performing a self-alignedsilicidation (salicide) process. In the salicide process, the SAB 222 isformed on the semiconductor substrate 200 for preventing a portion ofthe silicon material from being reacted in the salicide process. Then ametal layer (not shown) is formed on the semiconductor substrate 200 andfollowed by performing an anneal treatment to react the metal with theunderlying silicon. Since the salicide process is well-known to thoseskilled in the art, the details are omitted in the interest of brevity.As a result, the Schottky diode 206 is formed between the control gate210 and the SAB 222.

As shown in FIG. 3, the doped region 208 is formed under the Schottkydiode 206 and encompassing the entire bottom of the Schottky diode 206,the STI 220 is separated from the Schottky diode 206 and the dopedregion 208 by the well region 204 of the semiconductor substrate 202,and the control gate 210 is positioned between the Schottky diode 206and the STI 220. Additionally, another doped region can be formed underthe STI 220 in the well region 204. It is noteworthy that the controlgate 210 covers a portion of the Schottky diode 206, a portion of thedoped region 208 and a portion of the STI 220. Furthermore, the controlgate 210 including at least a gate dielectric layer 212, a conductivelayer 214 and a sidewall spacer 216 extending to cover a portion of theSTI 220 as shown in FIG. 3.

Please still refer to FIG. 3. The high voltage device 200 of thepreferred embodiment also includes a heavily doped region 224 having thesecond conductive type. The heavily doped region 224 is adjacent to theSTI 220, and particularly, is formed at a side opposite to the controlgate 210. That is, the heavily doped region 224 is separated from thecontrol gate 210 by the STI 220. Additionally, another salicide layer(not shown) is simultaneously formed on the heavily doped region 224 forimproving Ohmic contact.

According to the preferred embodiment, the Schottky diode 206 serves asan anode while the heavily doped region 224 serves as cathode. On theother hand, the Schottky diode 206, the control gate 210 and the heavilydoped region 224 construct a n-type metal-oxide-semiconductor (NMOS)device with the Schottky diode 206 and the heavily doped region 224respectively serve as the source and drain. It is noteworthy that aconventional silicon diode has a forward voltage drop of about 0.55-0.7V and the Schottky diode has a forward voltage drop of about 0.2-0.3 V.In this preferred embodiment, a forward voltage is applied to thecontrol gate 210 and thus a channel 230 is induced in the doped region208 under the control gate 210 as shown in FIG. 3, therefore the forwardvoltage drop of the Schottky diode 206 is further lowered. Consequently,the turn-on speed of the Schottky diode 206 is extraordinarilyaccelerated. On the other hand, when a reverse voltage is applied to thecontrol gate 210, the Schottky doped 206 is completely turned off.Briefly speaking, the control gate 210 is used to control the on/offstate of the Schottky diode 206.

Furthermore, since the forward voltage of the Schottky diode 206 islowered and the turn-on speed of the Schottky diode 206 is accelerated,when a feedback of high voltage is suddenly applied, the high voltagedevice 200 provided by the preferred embodiment is able to be turned onin time. Therefore the feedback is promptly bypassed through the highvoltage device 200 without impacting other devices. Accordingly, thehigh voltage device 200 of the preferred embodiment serves as aprotection device.

Please refer to FIG. 3 again. The high voltage device 200 of thepreferred embodiment further includes another heavily doped region 226having the second conductive type formed in the well region 204 underthe SAB 222.

Accordingly, the high voltage device 200 of the second preferredembodiment has improved turn-on speed and thus the high voltage device200 renders a protection function.

Please refer to FIG. 4, which is a schematic drawing of across-sectional view of a high voltage device having Schottky diodeprovided by a third preferred embodiment of the present invention. Asshown in FIG. 4, the high voltage device 300 includes a semiconductorsubstrate 302 having a first conductive type. In the preferredembodiment, the first conductive type is preferably a p-type. The highvoltage device 300 also includes a well region 304 having a secondconductive type, that is an n-type, formed in the semiconductorsubstrate 302. The well region 304 serves as a drift region, thereforethe doping concentration of the well region 304 is adjustable accordingto the requirement to the high voltage device 300.

The provided high voltage device 300 includes a Schottky diode 306formed on the semiconductor substrate 302 in the well region 304 and afirst doped region 308 formed under the Schottky diode 306 in the wellregion 304. The first doped region 308 under the Schottky diode 306further encompasses the entire bottom of the Schottky diode 306. It isnoteworthy that the high voltage device 300 of the preferred embodimentis provided in a symmetrical configuration with the Schottky diode 306and the first doped region 308 at the center as shown in FIG. 4, it canbe even in a circular configuration but not limited to this. The highvoltage device 300 also includes a control gate 310 encircling theSchottky diode 306 and the first doped region 308 and a dielectricregion such as a LOCOS or a preferably a STI 312 encircling the controlgate 310 in the well region 304 of the semiconductor substrate 302. Inother words, the control gate 310 is formed on the semiconductorsubstrate 302 and between the Schottky diode 306 and the STI 312.Furthermore, the control gate 310 covers a portion of the STI 312, aportion of the Schottky diode 306 and a portion of the first dopedregion 308 as shown in FIG. 4.

Please still refer to FIG. 4. The high voltage device 300 also includesa heavily doped region 314 encircling the STI 312 in the well region 304of the semiconductor substrate 302 and at least a SAB 316 positioned onthe semiconductor substrate 302. as shown in FIG. 4, the heavily dopedregion 314 is formed adjacent to the STI 312, and particularly is formedon a side opposite to the Schottky diode 306.

In the preferred embodiment, the Schottky diode 306 includes titaniumsilicide, cobalt silicide, tantalum silicide and combinations thereof.As mentioned above, the Schottky diode 306 is formed by performing asalicide process. And in the salicide process, the SAB 316 is formed onthe semiconductor substrate 302 for preventing a portion of the siliconmaterial from being reacted in the salicide process. Then a metal layer(not shown) is formed and followed by performing an anneal to react themetal with the underlying silicon. Additionally, another salicide layer(not shown) is simultaneously formed on the heavily doped region 314 forimproving Ohmic contact.

As mentioned above, since the Schottky diode 306 provides forwardvoltage drop lower than conventional silicon diode, the Schottky diode306 is integrated in the high voltage device 300 for lowering theforward voltage drop and improving the turn-on speed: The Schottky diode306, the control gate 310 and the heavily doped region 314 construct ann-type HVMOS device with Schottky diode 306 and the heavily doped region314 respectively serve as the drain/drain.

Please still refer to FIG. 4. The high voltage device 300 can furtherinclude a second doped region 318 formed under the STI 312. The seconddoped region 318 has the first conductive type, which is the p-type inthe preferred embodiment. By forming the second doped region 318, thehigh voltage signal from the heavily doped region 314 is enforced toacross a prolonged pathway, then reach the Schottky diode 306 andconverted into a lower applicable voltage signal. It is noteworthy thatthe amount of the resistors (not shown) is adjustable according to thedoping depth of the second doped region 318 as mentioned above.Accordingly, the well region 304 provides more voltage drops and thusthe high voltage device 300 has improved operating voltage.

Accordingly, the present invention provides the high voltage devicehaving the Schottky diode of the present invention, the advantagefeatures of the present invention includes high operating voltage andprevention of leakage current due to the provided first heavily dopedregion. According to another high voltage device having the Schottkydiode integrated with the MOS transistor, the advantage features of thepresent invention includes improved turn-on speed and thus such highvoltage device renders a protection function.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention.

What is claimed is:
 1. A high voltage device having Schottky diodecomprising: a semiconductor substrate; at least a dielectric regionformed in the semiconductor substrate; a Schottky diode formed on thesemiconductor substrate; at least a salicide block (SAB) positioned onthe semiconductor substrate; at least a first doped region having afirst conductive type formed in the semiconductor substrate, the firstdoped region being physically non-contacting with the Schottky diode; awell region having a second conductive type formed in the semiconductorsubstrate and the dielectric region, the Schottky diode and the firstdoped region are formed in the well region; a second doped region havingthe second conductive type formed adjacent to the dielectric region andon a side opposite to the Schottky diode in the well region, and thesecond doped region is a heavily doped region; and a third doped regionhaving the first conductivity formed under the dielectric region in thesemiconductor substrate, the third doped region being spaced apart fromthe first doped region.
 2. The high voltage device of claim 1, whereinthe SAB is positioned between the Schottky diode and the dielectricregion.
 3. The high voltage device of claim 2, wherein the first dopedregion is a heavily doped region formed under the SAB.
 4. A high voltagedevice having Schottky diode comprising: a semiconductor substrate; adoped region having the first conductive type formed under thedielectric region in the semiconductor substrate; at least a dielectricregion formed in the semiconductor substrate; a Schottky diode formed onthe semiconductor substrate; at least a salicide block (SAB) positionedbetween the Schottky diode and the dielectric region on thesemiconductor substrate; and at least a first heavily doped regionhaving the first conductive type formed under the SAB in thesemiconductor substrate, the first heavily doped region being physicallynon-contacting with the Schottky diode and entirely overlapped by theSAB.
 5. The high voltage device of claim 4, further comprising a secondheavily doped region having a second conductive type formed adjacent tothe dielectric region and on a side opposite to the Schottky diode inthe semiconductor substrate.